I have two cats and gave them both an application yesterday. I have used this product before (once) and had no reaction. I switched to flea collars and wish I had stayed with that choice. Anyway, one of my cats, Nina, started acting weird about an hour after application. She is a sensitive and high-strung cat anyway so I didn’t think she was acting that out of character. Until i noticed her breathing was very heavy and her eyes were dilated all the way. I immediately gave her a bath and washed that crap off of her. After that she started hiding whenever she could which was out of character. I know she felt vulnerable and scared b/c she is usually the alpha cat, the dominant one. She also was hissing a lot and doing loud cat moans. She was furious! I didn’t see any skin irritation but she was acting like I poured acid on her back. Anyway, I watched her all night and she slowly started turning back into her normal self. Less scared and she slept pretty well. Today I gave both of them a more thorough bath (not happy campers) and Nina seems ok. her back is still twitching here and there but I think she’s going to be OK. If this happens to your cats, wash the stuff off immediately with mild soap (like it says on the box) and monitor them closely. I bought this stuff to save a few bucks. (frontline can be costly) but it’s not worth my baby cat’s health. This stuff is poison and should be eliminated from the market. I am beyond pissed.